DAISY-10 is an RS485 half-duplex or RS422 full-duplex interface module with selectable opto-isolation and configuration via DIP switches. When configured in RS485 mode, up to 32 devies are pluggable on a single bus line.

Terminal Block Pinout

The bus line signals are available on a terminal block with 3.81mm pitch.

Pin

Signal

GND

GND signal when not isolated; external GND line when isolated

Y

RS422 TX+ line

Z

RS422 TX- line

B

RS422 RX- line or RS485 B line

A

RS422 RX+ line or RS485 A line

3V3

3V3 volt output when not isolated; external 3.3V DC line when isolated

DIP Switch Settings

Eight DIP switches allow you to configure your DAISY-10 module. To turn off isolation, you would set switches 1 and 5 to ON. Note: If you want to use isolated mode, you should remove LED D1 (3V3) from the board, due to a design flaw.

Switch

Function when ON

1

Wires internal 3.3V to screw terminal

2

Wires A to Y

3

Wires B to Z

4

Wires a 120Ω resistor between A and B

5

Wires internal GND to the screw terminal

6

Wires CPU RTS signal to DE IC driver

7

Wires DE to RE# on IC driver

8

Wires CPU CTS signal to RE# IC driver

Using DAISY-10 in RS485 mode

RS485, also known as TIA/EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. This communications standard is common in industrial automation because it can be used effectively over long distances and in electrically noisy environments.

Even though the data are transmitted over a 2-wire twisted pair bus, all RS485 transceivers interpret the voltage levels of the differential signals with respect to a third common voltage. Without this common reference, a set of transceivers may interpret the differential signals incorrectly.

The image below illustrates typical RS485 wiring in non-isolated mode (i.e., DIP switches 1 and 5 ON). For isolated mode, you will have to provide the 3.3V DC (and remove LED D1 from the board). Remember that the last node on the bus must have a 120Ω resistor for termination.

DIP Switch →

1

2

3

4

5

6

7

8

RS485 mode

ON

ON

ON

OFF

Isolated

OFF

OFF

Not isolated

ON

ON

A & B terminated

ON

A & B not terminated

OFF

RX disabled on TX

ON

RX always enabled

OFF

Using DAISY-10 in RS422 mode

In RS422 mode, set all DIP switches to OFF, except maybe 1 & 5 to turn off isolation. The image below illustrates typical RS422 wiring in non-isolated mode (i.e., DIP switches 1 and 5 ON). For isolated mode, you will have to provide the 3.3V DC (and remove LED D1 from the board).

RS485/RS422 Module Examples

These Python code examples run on the Terra Board with this module plugged into D10. You can modify the source code easily to run it on the Fox Board, e.g. change the port to D6.

The Daisy-10 class is a derived class from the pySerial where it is possible to call the serial ports also with the Daisy connectors name like D1, D10, etc instead of /dev/ttyS2, /dev/ttyS4 etc. Refer to the pySerial docs to learn more about its use: